100% renewable supply? Comments on the reply by
Jacobson and Delucchi to the critique by Trainer.

10.9.12

Ted
Trainer

I recently criticised the claim by Jacobson and Delucchi that renewable
energy sources could meet world energy demand. Jacobson and Delucchi replied defending their position. This
is a response to the main points made in that reply. The main issues are to do with
intermittency of renewable energy sources and the implications for redundant
plant and storage, vehicle to grid systems as a storage solution, the embodied
energy costs of renewable energy, and overall system capital costs. It is argued that Jacobson and Delucci do not provide satisfactory analyses of these
issues and that they do not show that energy supply can be 100% renewable. This discussion is intended to clarify
some of the core issues in the debate about the limits of renewable energy.

Several impressive documents have been published claiming to
show how world energy demand can be met by renewable energy sources, e.g., IPCC
(2011), Greenpeace, (2010), Beyond Zero Emissions (Wright and Hearps, 2010), Zero Carbon Britain 2030 (2007), Stern (2006), WWF (2010), and Jacobson and Delucchi (2011a, 2011b). There has been a strong tendency for
these to have been accepted as settling the issue,
especially among environmental theorists (e. g. Flannery, 2005), agencies
(e.g., the Australian Conservation Foundation) and Green political parties. Little critical analysis of the thesis has
been published, especially in academic and technical literature. Hayden, (2004), Bryce, (2004), and Moriarty
and Honnery, (2010) have put forward critical
arguments. Previous to Trainer (2007) Hayden’s book (2003, 2004) seems to have
been the only one published offering a critical view. Critiques of several of the above optimistic
reports are given at Trainer, 2012c. An attempt to develop a case regarding the global situation was given in
Trainer (2010) but for a significantly improved case see Trainer (2012).

My analyses have been offered as uncertain attempts to explore
the crucially important and neglected question of the limits of renewable
energy, which is likely to remain unsettled for some time to come. Apart from this reply by Jacobson and Delucci little or no critical comment on these analyses has
been received despite informal circulation encouraging independent evaluation. Unfortunately the reply by
Jacobson and Delucci does not deal satisfactorily
with the core issues. This
discussion of their reply enables further clarification and elaboration of the problems
and limits.

Integrating intermittent sources.

Jacobson and Delucchi argue that
problems of intermittency do not cause insurmountable problems for 100% renewable
energy supply. Their case in their
reply rests on reference to three main studies. Limited space and the insufficiency of
the information given do not permit a detailed examination of these cases but
it is appropriate to briefly note the kinds of problems they involve.

The analysis by Lund and Mathieson (2009) begins, as
renewable-optimistic analyses usually do, by making very optimistic assumptions
regarding achievable reductions in demand . (See for example Lovins,
2012,and Wright and Hearps, 2010.) It is not explained why the 2030
business as usual demand is expected to be only 11% higher than 2004 demand, or
why no further increase is expected between 2030 and 2050. It is claimed that a 50% reduction in
building heat, a 40% reduction in transport fuel and a 50% reduction in
household electricity consumption can be made by 2030. Further large reductions are
assumed between 2030 and 2050, including another 20% reduction in building and
heating and a further 10% reduction in electricity. These add to an assumed a 60% reduction
on the (questionably low) business as usual figure they state, despite assuming
large scale transfer of transport to electricity, use of hydrogen which is an
energy costly option, and the introduction of much dependence on electricity-driven
heat pumps. The target arrived at
is only 420 PJ/y (although the quantities in Fig. 6 add to 376 PJ/y).

In recent years it has been commonly assumed that business
as usual energy demand has been heading towards a doubling by 2050 (Moriarty and Honnery, 2010) and that GDP will more or less
multiply by 3 to 4. (Recent price rises and the GFC have reduced trend rates at
least in the short term.) However
this proposal implies that electricity demand can be cut to 20% of such a 2050
business as usual level, while the functions given to it are considerably
increased. No reasons are given to indicate that this is technically reasonable
or socially/politically plausible. At
least convincing answers and derivations that can be followed would be needed
before the target adopted could be regarded as acceptable.

Other but minor difficulties include the use of hydrogen and
fuel cells with no evidence given on energy losses, embodied energy costs and
capital costs, considerable use of biomass-gas-electricity generation with no
discussion of the total system energy efficiency (which is likely to be under
20% given that generation of the gas from biomass is at best around 57%
efficient according to Staubing, Zah and Ludwig, 2012,
p. 169, and the energy costs of producing and supplying the biomass would need
to be deducted from output), and considerable dependence on PV (1500 MW) and
solar thermal sources with no discussion of how the PV input is to be stored
and what contribution these two sources can be expected to make in winter when
demand is at its highest. Questionably
high conversion efficiencies are evident in Fig.6, 84% for hydrogen from electricity
and especially the 75% for fuels from biomass.

However these have not been the main problems in this study.
As is usually the case it deals only with annual average demand and supply
quantities and does not deal with the variations in these, especially winter
averages and extremes, and the implications for redundant plant. This is the crucial issue for renewable
supply and will be elaborated on below.

The study by Mathieson, Lund and Karlsson (2011) seems to use essential the same data as that by Lund and Mathieson,
although it reveals that 100 PJ/y is assumed to come from algae biomass. This is at least an uncertain prospect
given the unsolved technical problems, such as removing water from the biomass,
and providing the required very large carbon inputs in an economy that does not
have fossil fuel power generation supplying carbon. Again the crucial issues of guaranteeing
supply during conditions of extremely low renewable energy availability, required redundant plant and consequent capital costs are not dealt with.

The third major study is by Hart and Jacobson, 2011,
including a modeling study purporting to show that 99.8% of Californian delivered
energy could be produced from renewable sources. However an examination of the
information given shows that this initially impressive claim is highly misleading. As I have often pointed out it is not
difficult to explain how renewables can meet 100% of demand; what is difficult
is to explain how the huge amount of redundant plant required could be
afforded. This study makes no
reference to capital costs.

Hart and Jacobson do admit that the amount of capacity
required would be very large, but attention is not drawn to its magnitude or
significance. Table 2 on p. 2283 reveals
that to meet a 66 GW demand with low carbon emissions no less than 281 GW of
capacity would be needed. Included
in this is 75 GW of gas generating capacity, but this will be needed very
rarely to plug gaps in renewable supply. In fact it is stated that its capacity will be 2.6% (p. 2283) and it
will provide only 5% of annual demand. This means 75 power stations will sit
idle almost all the time.

In other words, to show that over a year renewable sources
can generate more than 95% of annual electricity requirements is not so impressive
or important. The important
questions are what amount of redundant plant would be needed to meet
electricity demand at every point in time, and what might the capital cost of
this be? Among other things, this would require detailed examination of supply
requirements through the most difficult periods of solar and wind availability.

Hart and Jacobson provide graphs (Fig. 4) showing how demand
might be met on four days during the year. These are far from difficult days for renewables, all four showing large
wind, PV and solar thermal contributions. It is remarkable however that the average gas contribution over these
four days is around 40% and greater than 50% on one, again making it difficult
to understand the Fig. 3 claim that gas would provide only 5% of electricity
demand, or to see how this proposal could be acceptable with respect to
emissions.

Thus Fig. 3a reveals the way renewable energy proposals are
typically misleading by setting out annual average contributions. It shows that (for minimum emissions)
solar is to provide 100,000 of the total 410,000 GWh required over a year. This gives
the impression that only enough solar plant will be needed to produce 100,000 GWh in a year. But when winds are low far more solar input (or gas input) will be
needed to plug the gap, and vici versa, meaning that
far more solar plant will be needed than Fig. 3a might suggest. Fig. 3b shows this, and as has been
noted the total comes to a remarkable system requirement that is four times as
much generating capacity as would be needed if it was all in the form of coal,
gas or nuclear plant.

Among the less important problems evident in the account is
the fact that the 2050 low carbon scenario assumes wind will provide 50% of
electrical supply. Although the
Danish and UK governments have announced 50% integration targets, the reviews (e.g., Lenzen, 2009) conclude that problems of integration might
limit the percentage to as little as 20%, except in unusual circumstances such
as in Denmark (below.)

It should also be noted that the debate is about whether or
not renewables can meet total energy demand, but the Hart and Jacobson paper is
only concerned with electricity demand, which makes up only around only
one-fifth of total demand.

Finally the 2050 scenario does not achieve a satisfactory
emissions regime. On p. 22 a 34% reduction is claimed but this is not likely to
be sufficient given that emissions from the other four-fifths of the economy
would have to be added, and given the probability that by 2050 all emissions
should be eliminated. (Meinshausen et al., 2009.)

It is clear therefore that this paper does not provide
impressive support for the claim that renewables can meet 100% of demand, let
alone that this could be afforded. Again the paper makes no reference to capital costs and the discussion
below shows these to be formidable at best.

The “big gap” weather event problem.

The discussion to this point has only been carried out in
terms of average or typical renewable energy availability, including average
winter values. What matters most, as
I stress in my analyses, is whether renewables can meet demand during “big gap”
events, i.e., periods of many days in which whole continental areas can
experience of calm and cloudy conditions. As my critique noted, Oswald (2008) documents a two week period in February 2006 in which Western Europe had negligible sun and wind and
UK electricity demand reached its highest peak for the year. Several similar documentations of the
magnitude of this phenomenon have been made in the renewable energy literature,
e.g., Soder et al., (2007), for West Denmark,
Sharman, (2005, 2011), Mackay, (2008), and Sharman, Layland and Livermore, (2012) for the UK, E On Netz, (2004)
for Germany, Davey and Coppin, (2003), Elliston (2012) and Lawson, (2011) for
Australia, Bach (2011) for five European countries and Flocard and Perves (2011) for seven, and Lenzen,
(2009). Proposals claiming that a region or a nation can depend entirely on
renewable energy are of little value unless they provide information on the long term availability of wind and solar energy with special
attention to the frequency and severity of these ‘big gap” events in the region.

The general response Jacobson and Delucchi make to the kind of evidence Oswald and others provide on these big gap events is
to say that their vision is for systems which extend beyond continental
boundaries. “…we have not claimed that WWS systems
must be self-contained within Europe; rather, we have explicitly talked about
much larger super-grids.” Reference is made to studies of such grids, for instance by Czisch (2004). There is no discussion of whether these studies show that very large
scale weather events can be overcome by such grids or at what cost. The review Flocard and Perves report on the intermittency problem in the
seven main European wind nations (2012) leads them to say, “Huge grid interconnectors between these seven
countries will not solve the problem resulting from insufficient wind
production during large climatic intervals.”

The most serious problem here is evident in the common
argument that “…the wind is always blowing somewhere.” The question is, where is it blowing right now? Are we to have built enough wind turbines to meet all demand in the place
where it is blowing today, and also to have built enough in the different region
which is the only place where it will be blowing next time there isn’t much
wind anywhere else, and so on...? When
the wind is blowing somewhere but there isn’t much wind anywhere the system
capacity is very low, and even if turbines have been built everywhere demand
can be met only if some non-wind sources of redundant capacity plug the gap. Obviously, the capital cost of building
enough turbines at all the places where the wind might be strong when it is not
blowing anywhere else would be unaffordable.

In addition such multi- or intercontinental proposals
involve significant transmission costs. If for instance Europe’s c. 340 GW
demand was to be met on some occasions such as Oswald documents from
Kazakhstan, and on some occasions from the Algerian coast and on some other
occasions from around Crete, the total length of transmission lines required
(at $.5 per km-kW, Harvey, 2011) would cost in the region of (at least) 340
million kW x 3 source regions x 5000km each x $.5) = $2.5 trillion, or around four
times the cost of 340 GW of local gas-fired power stations. To say the least
Jacobson and Delucchi do not (attempt to) show or
report that intercontinental supply visions are realistic or affordable. They refer to Czisch’s (2004) proposals, although these do not provide convincing answers to these
questions. Czisch notes that the cost of transmission lines from one solar thermal field in North
Africa to southern Europe could be equal to one-third of the field’s cost.

Again it is evident that the main problem is not explaining
how to meet large fractions of energy demand via renewables; it is whether the
amount of plant required could be afforded.

The significance of
Denmark.

Jacobson and Delucchi argue that
Denmark’s wind achievements show that these kinds of intermittency problems are
not very serious and do not set inconvenient limits to the integration of
renewables,. “...studies of Denmark alone at large penetrations of renewables ( [Lund and Mathiesen, 2009] and [Mathiesen and Lund, 2009]),
do not indicate the problems suggested by TT.” Of course they don’t, because Denmark
has nothing like 100% use of renewables and the modeling studies do not assume
such a situation. The debate is
about whether 100% is possible and little light is thrown on it by referring to
a country where intermittency problems have not been encountered as wind has
risen to generating electricity equivalent to only one fifth of power used and
c. 5% of energy used.

Lenzen’s review (2009) makes the
commonly recognised point that above a 20%
contribution from wind integration problems accelerate and in general the limit
seems to be well under 30%. Denmark
and the UK have stated that they aim to raise wind’s contribution to 50%, but
this does not mean that the goal is achievable. In Denmark’s case it might be given its
atypical circumstances. It is a
very small nation (5 million) with a low demand (c. 4 MW) close to large neighbouring countries (e.g., Germany 82 million) which are capable of absorbing surpluses. The country uses
considerable amount of energy for urban heating, enabling some surpluses to be
economically used. As the IPCC (2011,
p. 29) says re wind energy, Denmark has partly solved integration and
“curtailment” (dumping) problems “...by increasing flexible operation of CHP ...” Most
importantly its neighbours Norway and Sweden possess
large hydroelectric capacity that can in effect be used to store Danish electricity
exports (by phasing down hydroelectric output when wind imports from Denmark
are high.) Lund et al. (2010) argue that at present this does not have to be
done and that the reason why exports correlate almost perfectly with high
winds, as Bach (2012) and Flocard (2012) show, is
because it pays to keep Denmark’s efficient thermal power sources operating and
to export the surplus. Lund et al.
are saying that if the thermal sources were not that efficient they could be
phased down at times of high wind and the wind energy could be used rather than
exported. But this does not establish
that the integration problems associated with greater than 20% wind supply can in
fact be dealt with; it only makes clear that they have not had to be dealt with.

More important than the export issue would seem to be the
fact that times the Danish wind system is operating at around 3% capacity, (as are
the far bigger systems in six other European countries, see Batch, 2012, and Flocard and Perves, 2011.) Again this means that much alternative
generating capacity must be retained, and the capital cost implications of this
redundancy need to be taken into account when discussing the generalisabilty of the Danish system.

Another reason why Denmark is atypical is to do with its
access to large quantities of biomass. The proposal by Mathieson and Lund assume up to 333 PJ/y, (the
recommended scheme assumes 260 PJ/y.) This would be about 50% higher than would be possible per capita for all
the world’s anticipated 2050 population if the average of the estimates of
potential plantation plus waste biomass reported by the IPCC is assumed (and it
can be argued that biomass use should be kept far below this level; see
Trainer, in press.)

Mathieson and Lund also assume much use of electricity to
drive heat pumps in Denmark’s future, 445 MW. Mackay (2008, p. 152) shows that these
could not meet UK heating requirements in the UK due to the relatively low annual
rate of heat recharge from solar radiation.

To summarise, the reference to
Denmark provides little support for the 100% renewable claim, and their overall
case regarding intermittency falls a long way short of showing that this
problem can be solved, let alone at an affordable cost.

Storage in vehicle batteries.

The problem of intermittency would be significantly reduced
if not eliminated if large scale storage of
electricity was possible. Jacobson
and Delucchi argue that storage in electric vehicle
batteries can make a major contribution. They rightly point to some aspects of my critique which are
challengeable or mistaken, for instance they point out that batteries would not
need to be fully charged before use, nor to be recharged every day. However these points do little to
further their case and without adding to it they proceed to conclude,
“Reasonable inferences based on available data and our general understanding of
economics and consumer behavior suggest that V2G incentives, time-of-day
pricing, the wide range of types of EVs and recharging opportunities available
in a 100% WWS world, and consumer adaptation to new technologies will create
opportunities for substantial amounts of potential V2G energy storage.” This is an almost meaningless statement as
although there is no doubt that vehicle batteries will provide some storage
capacity everything depends on how substantial the amounts could be and no
quantitative estimate is given. There is reason to believe that it could not be very substantial.

The scale of the issue can be illustrated by considering the
present Australian energy pattern, in which transport accounts for 33% of final
use. Let us assume that 60% of this
can be converted to electric drives, and that this enables vehicle energy
efficiency to be cut by a factor of 4 as is commonly claimed. That would mean that the amount of
energy required to power electric vehicles would be around 5.5% of final energy
consumption. If on average battery capacity enabled (an unnecessarily generous) 3 days of car use storage
capacity would be c. 16.5% of final energy use. If on average batteries were kept
two-thirds fully charged, storage capacity available for non-transport use
would be around 5.5% of energy demand, i.e., c. 193 PJ/y or .53 PJ/d (and less
when losses in conversion into and from 240 voltage, and charging and
discharging losses are taken into account.) Australian electricity demand is approximately
2 PJ/d, so vehicle batteries could make a significant but not large
contribution to the 6 PJ storage task set by three days of poor weather.

Much the same conclusion comes from the study by Lund and
Kempton (2008) which Jacobson and Delucci refer to in support of their position. This is a valuable detailed analysis in which assumptions and derivations
can be clearly followed and factors such as the time vehicles are in use or
parked, or not plugged in, are taken into account. However the amount of storage demonstrated
is small in relation to potential storage need from the wider economy. They assume 30 kWh battery capacity, enabling
180 km travel. If we assume three times this capacity (which the authors
consider but say is not viable) 171 GWh could be
stored. If on average half this
capacity was available for storage use by the non-vehicular energy system it
would constitute only 70% of the average Danish daily electricity demand, and a
lower percentage of the winter average, let alone of a peak winter demand. Again this would be helpful but would
not make much difference in the kind of two week big gap
problem Oswald and others document.

It is important to briefly consider the logic of vehicle
storage here. Electric vehicle batteries are quite expensive and use scarce
materials, and their considerable weight detracts from vehicle energy
efficiency. The aim would therefore
be to equip vehicles with as little storage capacity as possible. The point of V2G systems is not to
locate storage capacity for the general economy on vehicles; it is to take
advantage of the storage capacity vehicles have for their needs but at times
are not using. The question then
becomes how much capacity for non-vehicle use would an efficient fleet be
capable of making available?

The weight of petrol plus tank needed to store 1 kWh for a 6
km trip would probably be well under 1 kg, but the battery weight required
would be around 7 kg. If a vehicle
was equipped with 90 kWh capacity the batteries would
weigh around 600 kg, doubling the weight of a light EV. As a petrol tank empties its weight
reduces, but this is not the case with batteries.

There is therefore a high priority on equipping vehicles
with just enough battery capacity to meet their typical needs. Most car journeys are quite short, and
if electric vehicles become the norm there will be recharging points at almost
every parking place, enabling minimal battery capacity to be carried. In addition there will be movement from
car use to “micro-travel” options, such as battery powered bicycles. Thus the majority of vehicle buyers might
be inclined to purchase a storage capacity of around 3 - 5 kWh, making Jacobson
and Delucchi’s 6 km/kWh assumption which would
suffice to get to the office or supermarket where recharging could take place
for the return journey. (For the
many very light vehicles used for short trips a much higher mileage would
apply, meaning even lower battery capacity.) If however we assume that an
average 10 kWh storage would suffice, the figures from Lund and Kempton
indicate that available storage in a Danish a V2G system might meet electricity
demand for only around 6 hours.

Vehicles needed for longer trips would not necessarily
improve the situation as these are likely to use
battery swap stations located at many points. (Note that battery swap systems would
more or less double the need for battery materials.)

Embodied energy costs.

Quite important for the discussion of capital costs is the
issue of the embodied energy costs of renewable technologies, or the energy
return they yield on the energy invested in their construction. This is generally regarded as being a
very important consideration, especially given marked declines in EROI for
conventional fuels in recent decades, and the relatively low EROI for renewable
energy technologies (except for hydroelectricity.) Some are concerned that there might be a
minimally viable EROI for high energy societies, and
that this might be in the region of 10, which is around the figure commonly
claimed for most renewables. (Murphy and Hall, 2010.) It is conceivable that embodied energy costs
alone could disqualify some renewable options, (see below.)

Nevertheless the full statement on the issue in the reply by
Jacobson and Delucchi is “… discussion of embodied energy is
irrelevant, because with an indefinitely renewable energy resource with no
external costs, the full lifetime cost as we have estimated is the relevant
factor—there is no additional pertinence to embodied energy per se.” The meaning intended here is far from
clear. Suffice it to say that the
contribution a renewable technology might make and its capital cost per unit of
energy provided must at least take into account the amount of energy needed to
produce the plant and deduct this from gross output to arrive at net
supply. Although the actual
proportion with respect to PV and solar thermal sources seems to be far from
settled, its importance is not in dispute. Some analysts argue that when the appropriate boundaries are taken and
all “upstream” factors are taken into account (i.e., the energy cost of the
smelters that produced the aluminium for PV panel
frames) the embodied energy cost of PV could be 30% and even 50%. (Crawford, et
al., 2006, Crawford 2011, Lenzen and Treloar, 2003.) If this is so the viability of these technologies is in serious doubt.

A dramatic illustration of the potential significance of
this factor is given by recent evidence on the energy cost of storing energy
via Ammonia dissociation. In
Trainer 2010 it was assumed that the most promising solar thermal technology
would be Big Dishes storing heat this way. However a recent discussion of the approach by those developing and
advocating it (Dunn, Lovegrove and Burgess, 2012)
reveals that for a 10 MW generator the storage system would require162 km of
30cm diameter steel gas pipe. (This
has been confirmed by personal communication.) The embodied energy cost of such a large
amount of steel, apart from construction, might approach 40% of plant lifetime
output. If so this would seem to
completely disqualify the technology from competing with central receivers or troughs
using conventional oil or salt tanks storage. This is a graphic demonstration of the
importance of taking embodied energy costs into consideration.

Capital costs.

The reply Jacobson and Delucchi give to my arguments re the crucial capital cost issue is given 243 words. The brevity seems to be due to the
extremely puzzling statement that they regard the issued as irrelevant. They begin by saying, “Estimates of the
total capital cost are relevant only if one argues that there are some
constraints on the availability of capital not adequately reflected in the
opportunity cost of capital. T11 makes no such claim, so this discussion is
irrelevant.”

Their subsequent comments not only fail to connect with the
core issue but misinterpret my critique. They say, “TT claims that we do not justify our assumptions regarding
capital costs…Our estimates of energy demand are
presented in Table 2 of JD11 and explained in detail in Appendix A.2 of JD11.
Thus, TT's claim that our estimate ‘…is not explained or justified’ is
untrue.” My point was not any
failure to provide documented cost information on specific technologies or
references to sources; it was to do with whether the conclusions drawn from
that information are misleading and my critique was that they are seriously
misleading mainly because they do not take into account the need for redundant
plant when estimating total system cost.

Occasionally the studies referred to make brief reference
to the crucial issue, the fact that that the systems envisaged would involve very
large amounts of redundant plant for generation and transmission. This is done by Hart
and Jacobson in the study discussed above, where it is said, “The low-carbon systems described in this
study require large capacities of dispatchable generation with very low capacity

factors... will also require significant investments
in transmission and distribution infrastructure...” (Hart and Jacobson, 2011, p. 2285.) However despite stating a capacity
required that is four times average demand no effort is made to assess the
overall system capital costs.

The focal concern in my attempts to assess the
potential and limits of renewable energy is the total system capital cost that
would be involved if the system is to be capable of
dealing with the intermittency of inputs. As has been shown above, that capacity requires substantial redundancy,
i.e., much plant of some kind to turn to when solar or wind or both sectors are
contributing little or nothing. Estimating the total system capital cost therefore involves adding the
capital cost of the quantities of all the various kinds of generating plant
that would be needed to cover these below average contributions from the
various sectors, along with the cost of other non-generation elements within the
systems, such as long distance HVDC transmission lines, any equipment for
hydrogen conversion, pumping, piping and storage, and the systems for growing
and delivering biomass to generating plants.

Jacobson and Delucchi do
not deal with this issue; they do not attempt to estimate the amount of
redundant plant required or its aggregate capital cost. How, for instance, would the total
capital cost of a system requiring 281 GW of renewable generating capacity
compare with the total capital cost of a system requiring 66 GW of coal-fired
capacity? Note that the calculation must take into account the fact that 1kW (peak)
of coal-fired capacity generates on average .8 kW but 1 kW of solar thermal or
PV (peak) capacity, costing at least twice as much, generates on average only
.2 kW.

Fig. 3 from Hart and Jacobson shows that in their
proposal 110 GW of solar and 75 GW of wind capacity would be needed. These quantities indicate a capital cost
of around $ 600 billion, for two thirds of the capacity needed. To meet the demand via gas-fired plant
might cost c. $70 billion. (It
seemed above that the proposal actually assumed/required sufficient gas
capacity to meet all demand.) This aligns with my general finding that 100%
renewable energy supply systems are likely to involve capital costs well
in excess of ten times the present capital costs of energy supply.

These considerations show why it is highly misleading to analyse system costs in terms of levelised costs. The latter figures only indicate the cost of energy from a technology,
such as wind or PV, when all its lifetime construction, operations, interest
etc. costs are divided by its lifetime output. Such a figure tells us nothing about how
many extra turbines, or solar, coal, gas, oil or nuclear generating plants must
also be built to provide a system with the back-up capacity that will enable
the wind sector to meet its average contribution when there is little or no wind. As Lenzen (2009) points out, the cost of a sector’s back-up plant should be added to the
cost of that sector, just as the cost of a home PV system should include that
of the emergency petrol generator.

It is puzzling that Jacobson and Delucchi seem dismiss the significance of this distinction. Their full response on the levelised cost point is, “T11 concludes that ‘the common practice
of focusing on levelised costs in estimating total
system capital costs leads to serious underestimation of system costs.‘ This is
incorrect. Levelised costs are based on the estimated
capacity factor, where the capacity factor is what would be obtained in an
optimized system (i.e., the least-cost system that reliably satisfies demand).
This is part of a correct and complete estimate of the average energy cost of
the system; there is in principle no underestimation whatsoever.” Apart from the problem of grasping what
is being said here, there is no recognition of a redundancy problem or its
implications for total system capital cost. Nevertheless Jacobson and Delucchi conclude, “In sum, T11 provides no valid criticism
of the detailed methods or assumptions of our analyses of energy cost and
energy demand.”

My initial attempt
to frame an approach to assessing the viability of a global 100% renewable
energy supply in view of these intermittency and redundancy issues (Trainer
2010) could only be based on data regarding solar thermal power that was not
very satisfactory and probably arrived at a cost conclusion that now appears to
have been considerably too high. Since then more confident assumptions have been enabled by the
publications by Hearps and McConnell, (2011), Lovegrove et al. (2012), AETA, (2012), and especially the
NREL (2010, 2011) SAM packages. (Contrary
to my 2010 impression these seem to clearly establish central receivers as much
more viable than Big Dishes with Ammonia storage capacity.) Trainer (2012e) uses these sources in an
improved exploration of four possible strategies for a global 100% renewable
energy supply, and concludes that the annual capital investment required would
be in the region of ten times as great as it is at present, even without
including several important cost factors which cannot be quantified satisfactorily.

Conclusions

The assessment of the limits of renewable energy has been a
neglected issue but it is of the utmost importance as crucial
and costly policy decisions will have to be made in the near future, e.g., between
nuclear, fossil fuel with CCS and renewable paths. Unfortunately the reply by Jacobson and Delucchi is not very helpful in clarifying the core
issues. In my view they do not put
forward a satisfactory case for their claims and do not deal satisfactorily
with the criticisms of their position I originally published. Nevertheless in my view the exchange
contributes to the clarification of the field. Following are the issues on which further
analyses might best focus.

Analysis of long term weather records over large regions to
establish the frequency and magnitude of ”big gap” events for wind and solar
energy, and most importantly, for coincidences of these, i.e., times when
there is negligible wind or solar energy available.

Use of such data to
estimate the large scale or intercontinental location patterns for wind and
solar generation most likely to be able to provide through periods of low
or negligible combined wind and solar energy, and estimates of the redundant
plant required, for the required transmission networks and for the
associated capital costs.

More thorough studies
leading towards agreed estimates of embodied energy costs, including
established conventions re the accounting of system boundaries and
“upstream” costs.

More confident analyses of
the probable impact of rising energy and resource costs, multiplying the
cost of inputs to the construction of renewable plant and requiring
adjustment to current estimates of future capital costs.

Attempts to assess the
potential impact of possible future trends within global economic
conditions on the viability of investment in renewable energy. If difficult times persist and if
as is argued above the required investment sums will be far more
substantial than has been assumed, are they likely to be forthcoming in an
era in which capital is likely to be scarce and increasingly wary of risky
ventures, and in which continued investment in fossil fuels is likely to
be a more attractive energy option?

Recognition that the
crucial issue is not showing how 100% of supply can be provided from
renewable sources, but exploring whether the capital cost is likely to be affordable.